Natural swinging period of a two-rod leg model

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sungjoooneee
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The human leg can be compared to a physical pendulum, with a "natural" swinging period at which walking is easiest. Consider the leg as two rods joined rigidly together at the knee; the axis for the leg is the hip joint. The length of each rod is about the same, 54 cm. The upper rod has a mass of 7.0 kg and the lower rod has a mass of 4.3 kg.

Calculate the natural swinging period of the system.
Express your answer using two significant figures.

I really need help..i am totally lost and it;s due in 3 hours...
 
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sungjoooneee said:
The human leg can be compared to a physical pendulum, with a "natural" swinging period at which walking is easiest. Consider the leg as two rods joined rigidly together at the knee; the axis for the leg is the hip joint. The length of each rod is about the same, 54 cm. The upper rod has a mass of 7.0 kg and the lower rod has a mass of 4.3 kg.

Calculate the natural swinging period of the system.
Express your answer using two significant figures.

I really need help..i am totally lost and it;s due in 3 hours...

Show some effort first!

I haven't seen this two pendulum system before but you must show your work before anyone else would help you (see rules).

I can say assume it as one rod and find center of mass
using the pendulum equations (that mgl = something .. I don't have my book near me for reference and I cannot remember those standard equations correctly) find T. (but this is just a guess)
 
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The lower leg will move about the knee at the endpoints of the swings and for one of the 2 swings in particular. Since there is no air resistance, you may avoid working with that; what you might want to take into account towards are fluctuations in the moment of inertia and see if there is any effect on the overall rotation.
 
T = 2pi Squareroot (I//mgh)

how do you determine moment of inertia, and h..

For m do i use 7.0 kg or 4.3 kg